P708: HIGH MUTATIONAL CONCORDANCE IN PAIRED BONE MARROW AND PERIPHERAL BLOOD SAMPLES IN PATIENTS WITH CONFIRMED OR SUSPECTED MYELODYSPLASTIC NEOPLASM
Authors: Natalie Wossidlo, Sandra Huber, Torsten Haferlach, Manja Meggendorfer, Stephan Hutter, Gregor Hoermann, Isolde Summerer, Henning Ruge, Constance Baer, Wolfgang Kern, Claudia Haferlach
Journal: HemaSphere (2023)

Background: Bone marrow (BM) aspirates are so far required for morphological and genetic assessment in patients diagnosed with myelodysplastic neoplasms (MDS). Further evaluation of unexplainable cytopenia and the development of novel disease-modifying agents for MDS require more frequent BM sampling to assess response to targeted therapies. As frequent BM sampling is inconvenient and has been associated with some morbidity, evaluating replacements for BM aspirates is desirable. Aims: Evaluate the utility of peripheral blood (PB) for mutational analysis in suspected or confirmed MDS to omit the need for BM sampling by comparing concurrent PB and BM samples. Methods: We analyzed 150 patients with paired BM and PB samples with both materials taken either on the same day (n=100; group 1) or within less than 15 days (n=50; group 2) including 48 patients with confirmed MDS according to WHO 2017. All samples were subjected to targeted panel sequencing, evaluating mutations in 40 genes associated with myeloid neoplasms. Mutations were assessed as positive at variant allelic frequencies (VAFs) >1%. Results: At least one mutation (MUT) was found in 97/150 (65%; 92% in confirmed MDS) patients (median MUTs/patient: 2; range 1-10), while BM and PB samples of 53 patients (group 1/2: 37/16) did not show any MUT in any of the 40 analyzed genes (Figure). In total, we detected 257 MUTs affecting 28 of the analyzed genes. Most frequently, MUTs in TET2 (n=44; 17%), DNMT3A (n=23; 9%), or ASXL1 (n=22; 9%) were found. In 90/97 (93%) patients, identical MUTs were seen in BM and corresponding PB. In only one patient no mutation was detected in the PB while the corresponding BM showed a DNMT3A mutation (VAF: 9%). In 4 additional patients, the number of MUTs per patient was higher in BM, while in two patients more MUTs were found in PB. Of all detected MUTs (n=257), 247 (96%) were found in both BM and PB (BM VAF ≥13%), while 8 (3%) and 2 (1%, both DNMT3A) MUTs where only detected in BM (BM VAF <13%) or PB (PB VAF ≤4%), respectively. Thus, all MUTs with a BM VAF ≥13% were detected also in corresponding PB samples, while 98/106 MUTs (92%) with a BM VAF <13% were also found in PB. Furthermore, the time difference between sampling did not impact on discordant MUT detection. For 138/257 MUTs (54%) equal VAFs were seen in BM and PB (VAF difference <5%), while for 119 (46%) VAF was higher in BM compared to PB. Overall, the median VAF was higher in BM compared to PB across all genes (overall median VAF difference: 6%; range: 2-23%; p<0.001; Figure). Interestingly, the median VAF difference was lower in group 1 compared to group 2 (median VAF difference: 3% vs. 6%; p=0.04). The finding of at least one somatic MUT as an important diagnostic marker of clonality was consistent between PB and BM in all but one patient. When excluding 14 patients with previously diagnosed myeloid neoplasm, this corresponds to a clinical sensitivity of 98.8%, a clinical specificity of 100%, a positive predictive value (PPV) of 100%, and a negative predictive value (NPV) of 98.1% for the detection of clonality in PB only compared to BM as the gold standard. Summary/Conclusion: We found a high concordance of individual mutation detection (96%) in paired BM and PB samples in patients with suspected/confirmed MDS with a slightly higher median VAF in BM. Importantly, PB showed a high PPV and NPV for the clinically important question of NGS-based clonality assessment in patients with unexplained cytopenia. Our data indicate that regarding mutational analysis PB may serve as reliable surrogate obviating the need for frequent BM sampling.Keywords: Peripheral blood, Bone marrow biopsy, Mutation analysis, MDS